Well it depends but u need to know that people like that are usually unhappy or have pathetic life so they need to vent or belittle others to feel better. So u can basically call them out like "hmm what a pathetic life u must have to do things like this to feel better" and that's where u stop and ignore them, trust me it pisses them off, and they will try to continue to argue but they'll never win. Also if you want to have some inner peace, try to take control of the convo, by joking about your own stuttering shows that you're not bothered making their jokes or comments useless, since most of those comments or jokes are attempt to provoke you, from my own experience they don't find that funny. And most of normal people don't like people that make jokes about stuff like that. Also cheap tricks works like "sorry i didn't hear ya can u speak louder" or "oh i didn't know u also stutter" Or if u wanna prove they are below u, u simply ignore them and leave. All in all u got to realise there will always be people like that and the sooner you accept that it's a part of life and that stuttering is something that's a part of you it will bother you less.